//你的代码将被嵌在这里
#include <iostream>
#include <cmath>
using namespace std;
class Point
{
private:
    double x, y,d;
public:
    Point():x(0),y(0),d(0){}
    void setPoint()
    {
        cin>>x>>y;
    }
    double Distance(const Point t)
    {
        d=sqrt(pow(x-t.x,2)+pow(y-t.y,2));
        return d;
    }
};


int main()

{

    Point a,b;

    a.setPoint();

    b.setPoint();

    cout<<a.Distance(b);

    return 0;

}